Process for dewaxing mineral oils



June 30,'1942.` DLG. BRANDT PROCESS FR DEWXING MINERAL OILS Filed May11, 1938 Kul-...IU v ...93.1

xml-...IU

mw/opm, u z n Oma A Wn@ INVENTOR Almut.

lslvfmd v x ATTQRNEY Patented June 30, 1942 PROCESS FOR DEWAXENG MHNERALOILS David G.V Brandt, Westfield, N. J., assignor to Cities Service OilCompany,- New York, N. Y., a corporation of Pennsylvania Application May11, 1938, Serial No. 207,232 4 Claims. p (01.196-18) This inventionpertains to a process for dewaxing petroleum oils, and more particularlyto the dewaxing of petroleum lubricating oil stocks.

The invention of the present application is an improvement on theprocess of the applicants` pending application Serial No. 670,066, filedMay 9, 1933, for improvements in the Art of dewaxing oils. The saidapplication discloses a process for dewaxing petroleum oil stocks to beused for lubricating purposes in which the stock is dissolved in aliqueiied normally gaseous hydrocarborn diluent such as liquid propaneor any similar hydrocarbon or mixture having less than ve carbon atomsto the molecule. In that process a portion of the chilling is eected byvaporizing some of the solvent, although provision is made for mixingprecooled diluent such as liquid propane with the oil solution atvarious stages of the chilling operation.

In carrying out the chilling process in accordance with the disclosureof said application, the oil-propane mixture is passed through a seriesof chambers and additional quantities of cold liquid propane is added tothe mixture for the purpose of maintaining the desired gravity andviscosity of the oil mixture. After the precipitation of the Wax in theoil solution, the wax is separated by gravity separation in anexternally cooled separator in which provision is made for acceleratingthe removal of wax.

Repeated tests have shown that in the dewaxing of petroleum oils inwhich propane is used as a diluent and internal refrigerant, thechilling of the mixture by vaporizing propane apparently breaks up thewax crystals or prevents the formation of large wax crystals because ofthe intense agitation of the oil due to the vaporization of the propane.

Therefore, the primary object of the present invention is to provide animproved process for the use of a low molecular weight diluent such asvliquid propane in which the wax precipitation will be greatly improved.

A further object of the invention is to provide an improved apparatusparticularly adapted for carrying out the improved process of thepresent invention,

With these objects in mind the process of the present invention ingeneral comprises the steps of forming a solution of the petroleumlubricating oil stock to be dewaxed in liquid propane or similar lowmolecular weight hydrocarbon, cooling the solution by indirect heatexchange with .a cooler i'luid to Aa point just short of wax precooledsolution into a chilling zone maintained at a pressure adapted toprevent 'vaporization of the diluent and introducing prechilled diluentinto the solution in sufficient quantity to eiect the precipitation ofall of the wax content of the oil desired to be removed therefrom, theintroduction of the chilled diluent being effected in such a manner asto cause only a mild eddying of the oil mixture to bring it and theintroduced diluent to equilibrium temperature conditions. After the waxhas been precipitated in the manner described, it may be separated fromthe diluted mixture by settling, centrifuging or ltering, or anycombination of these common practices.

Other objects, features and advantages of the process and apparatus ofthe present invention will be apparent to those skilled in the art fromthe following more detailed description thereof taken in connection withthe accompanying drawing in which:

The single ligure is a diagrammatic flow sheet of apparatus particularlyadapted for carrying out the improved process, and in which certain ofthe elements of the apparatus are shown in vertical position.

Referring to the drawing, the oil stock to be dewaxed is conductedthrough a line I, and introduced into a mixer 2 where the voil is mixedwith liquid propane introduced through aline 3. A solution of the oilstock in propane is effected in the mixer 2 and the resulting solutionis passed from the mixer downwardly through a heat eX- changer column 4,rst in indirect heat exchange with a cooling liquid such as Water whichis passed through a cooling coil 6, and then in heat exchange with arelatively cold liquid Vsuch Aas cold dewaxed oil which is passedthrough a heat exchange coil 8. The diluted oil stock introduced intothe tower i may contain about 50% of liquid propane, and'may be at aninitial temperature of from 125 F. to about 145 F. or at the temperatureof the solution leavingthe mixer 2 in which the oil stock was broughtinto'solution with liquid propane. In some'cases particularly where thetemperature of the oil or propane is too low, Vit is necessary to heatthe oil or propane, or both, to the temperatures referred to, inv orderto eliect thorough solution of the oilstock in the propane. The dilutionat this point should not be greater than necessary to insure easyhandling of the oil stock at temperatures approaching its pour point,orlthe Vpoint at'which Wax Would begin to precipitate out. However, `theoil mixture should contain at least 30% or 40% of Vcipatition in thesolution, thereafter passing the :55 DlOpane at this Stage 0f theOperation.

The oil stock mixture passed through the cooling tower 4 is cooled to atemperature just above that at which wax precipitation would take place,and then conducted through a valved line I@ into a compartmentedchilling chamber I2, in which vaporization of propane is prevented andin which the compartments are merely separated by baiiles around whichthe oil mixture passes. As the oil mixture enters the rst compartment,it is mixed with a proportion of cold liquid propane which is usedexclusively as the cooling medium for precipitating the wax. As the oilmixture passes through the compartments of the chilling cha-mber I2 itis cooled to successively lower temperatures at any desired rate by theintroduction of increments of extremely cold propane through a pluralityof valved injection lines I4. In each compartment the cold propane isinjected through an injector type of nozzle which prevent-s shockchilling by creating a flow of the oil mixture past the nozzle and byproducing a gentle circulation of the mixture in each compartment. Thismethod vof injection insures thorough mixing of the cold propane and theoil stock mixture without causing any substantial agitation of themixture which would tend to break up the wax crystals as they form,

`Oil stocks which are more effectively handled by rapid chilling, may bechilled almost instantaneously in a single compartment of the chamber I2or in a single chilling chamber, by rapidly mixing with the oil stockmixture the required amount of extremely cold liquid propane. The seriesof compartments in the chilling chamber I2 maybe utilized to eiectgradual chilling of the oilstock and the gradual building up of the waxcrystals as the mixture advances through the chamber. The oil stockmixture in the chamber I2 may be cooled to a temperature of 20 to 40 F.or to any other temperature found to be necessary for completelyprecipitating the wax content desired to be removed from any selectedoil'stock under treatment.

The chilled oil mixture containing the precipitated wax in suspension isconducted from the chilling chamber I2 through a valved line I6, Yandforced by means of a pump II, or passed through a valved by-pass lineVI3 vand a line I9 into a wax separating apparatus 20 in which the waxis removed-from the diluted oil mixture. The apparatus '20 may 'compriseany suitable wax separating equipment suitable for the particular stocksuch as 'centrifuged lters, or settling chambers. The separated wax isconducted from the apparatus 20 Vthrough a line 22 into a wax washingunit 24, while the wax-free oil solution is conducted through a line 26and passed by means of a pump 28 and 'a line 30 throughthe heatexchanger coil 8 mounted in the cooling` tower 4.

While it is not necessary to ymaintain a superatmospheric pressure on apropane oil solution at temperatures below about 40 F. to preventvaporization of propane, substantial pressures are maintained on the oilmixture in the cooling tower 4, the chilling chamber I2 and the waxseparating apparatus 20, in order to prevent any evolution of vapor. Thepressure required in the cooling tower 4 and chilling chamber I2 willdepend upon the temperature of the mixture as introduced into thesechambers Aand must be sufciently high to maintain the propane in liquidphase. Except for natural pressure drop due to flow resistance throughthese-elements of the apparatus, the same pressure -may be employed,

but a slightly lower pressure may be used in chamber I2. The valve inline I6 may be used to reduce the pressure a substantial degree, butwhere lter presses are used the pressure for effecting the ltrationoperation may be derived from the high pressure in the chamber I2 andtower 4 by-passing the pump I1,

The cold liquid propane used in effecting the chilling operation in thechamber I2 may be obtained by the auto-refrigeration of liquid propaneinitially at atmospheric temperatures. For example, liquid propane atatmospheric temperature is conducted from a propane storage 32, which ofcourse will be maintained under suitable superatmospheric pressure toretain the propane in liquid state, through lines 34 and a series ofindirect heat exchange coolers 36 and 38, and through a pressurereducing valve 40, into a propane chilling chamber 42. The expansion ofthe propane into the chamber 42 vaporizes a portion of the propane andchills the remaining portion; and the temperature to which the remainingliquid is reduced may be controlled by the pressure maintained in thechamber 42. The vapor evolved. upon the p ressure reduction in the.chamber 42 is ,conducted through a valved line 44 and through theseries of heat exchange coolers 38 and 36 by means of lines 46 and 48.The vapors evolved in the chamber 42 are naturally much cooler than thatof the liquid propane prior to expansion, so that it is an ideal coolingagent for precooling the liquid propane in the coolers 36 and 38. Thepropane vapor in the line 48 is picked up by a compressor 50 whichcompresses the propane to a 'high superatmospheric pressure and forcesit through a line 52, a condenser 54 and a line 56 into the propanelstorage 32. 4In this operation the pressure in the storage chamber 32is maintained by the compressor 56. Propane from an outside source maybe introduced into the system through a valved line 58 which connectsinto the line 52. A vacuum of any desired degree may be maintained onthe `propane chiller 42 by the suction created by the compressor 50, sothat the liquid propane obtained in Chiller 42 may have an extremely lowtemperature such as for example minus 55 F. to minus 85 F.

:The cold propane distributed through the injection lines i4, is drawnfrom the Chiller 42 through a line 60, and forced by means of a ypump 62and a valved line 64 into any or all of the Vlines I4 which may be inuse for supplying cold propane to the oil stock mixture passing throughthe chilling chamber I2. Liquid propane from the chiller 42 may also beutilized in washing the oil from the wax in the washing unit 24 bymerely withdrawing cold liquid propane from the line 64 through a valvedline 66 which connects into the washing unit 24. The cold propane and.oil washed from the wax in the unit 24 is removed through a valved line68, while the washed wax is removed 'through a line 16. The coldoil-propane mixture from the line 68 maybe introduced into any orall ofthe lines I4 and used as a chilling medium. The wax or wax slurrydischarged through the line 22 is at a very low temperature and the coldliquid `propane introduced through the line 66 .is also at a very vlowtemperature, so that the maintenance oflsubstantial pressures .in thewax .Washing unit 24 is .not necessary.

In .the dewaxing of many petroleum oil stocks, it isprefera'ble tomaintain the dilutionof rthe stock as low as reasonably possible untilthe wax precipitation is' substantially complete, in order to insure theformation of relatively large wax crystals. Some stocks may not requirevery low temperatures in the chilling chamber l2 in order to precipitatethe wax desired to be removed therefrom, but relatively low temperaturesare usually necessary in order to prevent any rise in temperature abovea certain maximum during the wax separation step. Minimum chilling forprecipitation may be effected in the chamber I2 by the addition ofextremely cold liquid propane, and the additional chilling necessary maybe effected by conducting the oil stock mixture containing theprecipitated wax from the line I6 through a connecting valved line 'I2into a flash chilling chamber M in which the additional chilling iseffected by vaporization of a portion of the liquid propane diluentunder reduced pressure. In this operation, the vaporized propane isconducted from the flash chiller 14 through a valved line 'I5 into theline Q4, and the chilled wax-stock mixture at the desired lowtemperature is conducted through a line i8 into the line I6 beyond thevalve, and forced by means of pump l1 into the dewaxing apparatus 2D.The temperature to which the oil stock is chilled in the chiller 14 iscontrolled by the pressure or vacuum maintained in this chamber, byregulating the Valve in line 16.

Where it is necessary to chill the oil stock solution to extremely lowtemperatures for the p-recipitation of the wax content, a portion of theprecipitation may be eiected in the chilling chamber i2 and theremaining portion in the iiash chiller lli in order to avoid excessivedilution of the mixture during the wax precipitating operation. However,it is preferred to effect all of the wax precipitation in the chamber l2under conditions such that there will be no agitation suicient to breakup wax crystals as is usually the case where prop-ane vaporization isrelied upon for chilling and precipitating purposes.

While various modifications may be made in the improved process andapparatus, as described above, the primary feature of precipitating thewax by addition of cold diluent has been found to materially increasethe wax precipitation for a given chilling temperature and facilitatethe separation of the precipitated wax. While liquid propane has beenreferred to as the diluent and chilling agent in the example, it is tobe understood that other similar hydrocarbons or other compounds of lowspeciiic gravity may be employed, and the hydrocarbons may be saturatedor unsaturated hydrocarbons preferably of lower molecular weight thanbutane.

1t is to be understood that in utilizing the apparatus, all elements,lines and pumps will be insulated where the temperatures therein arebelow normal.

Having thus described the invention in its preferred form, what isclaimed as new is:

1. In the process of dewaxing petroleum lubricating oil stocks in whichthe oil stock to be dewaxed is diluted with liquid propane in suicientquantity to completely dissolve the oil stock and provide a solutionwhich will be fluid and readily handled at temperatures below the pourpoint of the oil stock, the improvement which comprises cooling thesolution by indirect heat exchange with a cooler low gravity liquid to atemperature just short of that of wax precipitation in the solution,thereafter passing the oil mixture to be dewaxed through a series ofrelatively large zones in which the mixture is gradually chilled toprogressively lower temperatures by mixing therewith precooled liquidpropane under conditions adapted to prevent vaporization of any of thepropane, introducing the cooled propane into the oil mixture in eachzone in a jetting action adapted to cause only mild eddying currents ineach of said zones to effect equilibrium between the oil mixture and theintroduced cold propane, maintaining a superatmospheric pressure in eachzone and preventing substantial agitation therein, introducing asuiicient proportion of cold liquid propane into said zones tocompletely precipitate the wax content of the oil desired to be removedtherefrom by the time the oil has passed through said series of zones,and separating the precipitated wax from the resulting chilled oilmixture to produce a dewaxed petroleum lubricating oil stock.

2. The process of dewaxing petroleum lubricating oil stocks in which theoil stock to be dewaxed is diluted with a liquefied normally gaseoushydrocarbon which is liquid at low dewaxing temperatures, saidhydrocarbon being used in sufficient proportion and under conditionssuch as to completely dissolve the oil stock and provide a solutionwhich will be uid and readily handled at temperatures at and somewhatbelow the pour point of the stock, thereafter passing the dilutedmixture -to be dewaxed through a series of relatively large chillingZones through which the mixture is passed in series and graduallychilled by mixing therewith in each zone an increment of precooledliquid normally gaseous hydrocarbon, maintaining a substantial body ofthe mixture being chilled in each zone, introducing the precooled liquidnormally gaseous hydrocarbon into the oil mixture in each zone in ajetting action adapted to cause only a gentle local circulation of themixture therein to eect equilibrium between the oil-mixture and theintroduced cold hydrocarbon, maintaining a superatmospheric pressure ineach Zone sufficient to prevent vaporization of any of said hydrocarbonand preventing substantial agitation in said zones, introducing asuii'icient proportion of the cold normally gaseous hydrocarbon intosaid series of Zones to completely precipitate the Wax content of theoil desired to be removed therefrom by the time the oil mixture haspassed through said zones, and separating the precipitated wax from theresulting chilled oil mixture to produce a dewaxed petroleum lubricatingoil stock.

3. The process of dewaxing petroleum lubricating oil stocks in which theoil stock to be dewaxed is diluted with a liquid normally gaseoushydrocarbon which is liquid at wax separation temperatures, diluting theoil stock with a sufcient proportion of said hydrocarbon and under suchconditions as to completely dissolve the oil stock and provide asolution which will be fluid and readily handled at temperatures as lowas the pour point of the stock, thereafter passing the solution to bedewaxed into one end of an enlarged elongated chamber and then through aseries of distinct cooling zones in said chamber, maintaining asubstantial body of the mixture in each zone, gradually chilling themixture as it passed through said series of zones in said chamber bymixing with the body of material in each zone an increment of extremelycold liquid normally gaseous hydrocarbon thereby gradually building upwax crystals in the mixture as it advances through said chamber,introducing the cold hydrocarbon into the b-ody of oil mixture in eachzone in a manner adapted to cause only a gentle local circulation of themixture therein to eiiect. temperature equilibrium between the oilmixture and the introduced cold hydrocarbon, maintaining asuperatmospheric pressure in said chamber suicient to preventvaporization of any of said hydrocarbon and preventing substantialagitation of the mixture in said chamber, said hydrocarbon introducedinto said zones being of sufciently low temperature and of sufficientproportion to completely crystallize and precipitate the Wax content ofthe oil desired to be removed therefrom during the passage: of the oilthrough said chamber, discharging the chilled mixture from said chamberand separating the precipitated wax therefrom to produce a dewaxedpetroleum lubricating oil stock.

4. The process of dewaxing petroleum lubricating oil stocks as definedby claim 3 in which said chamber is a vertical chamber and the solutionto be dewaxed is introduced into the upper part thereof, and in whichsaid zones are dened by vertically spaced baies in said chamber aroundwhich the oil mixture ows toward the bottom of the chamber.

DAVID G. BRANDT.

